plucky (3) MPI_Request_free.openmpi.3.gz

Provided by: openmpi-doc_5.0.7-1_all bug

SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Request_free(MPI_Request *request)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_REQUEST_FREE(REQUEST, IERROR)
               INTEGER REQUEST, IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Request_free(request, ierror)
               TYPE(MPI_Request), INTENT(INOUT) :: request
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT/OUTPUT PARAMETER

request: Communication request (handle).

DESCRIPTION

       This operation allows a request object to be deallocated without waiting for the associated communication
       to complete.

       MPI_Request_free marks the request object for deallocation and  sets  request  to  MPI_REQUEST_NULL.  Any
       ongoing  communication  that is associated with the request will be allowed to complete. The request will
       be deallocated only after its completion.

NOTES

       Once a request is freed by a call to MPI_Request_free, it is not possible to  check  for  the  successful
       completion  of  the associated communication with calls to MPI_Wait or MPI_Test. Also, if an error occurs
       subsequently during the communication, an error code cannot be returned to the user — such an error  must
       be  treated  as fatal.  Questions arise as to how one knows when the operations have completed when using
       MPI_Request_free. Depending on the program logic, there may be other ways in which the program knows that
       certain  operations  have  completed  and this makes usage of MPI_Request_free practical. For example, an
       active send request could be freed when the logic of the program is such that the receiver sends a  reply
       to  the  message  sent  — the arrival of the reply informs the sender that the send has completed and the
       send buffer can be reused. An active receive request should never be freed, as the receiver will have  no
       way to verify that the receive has completed and the receive buffer can be reused.

       Example:

          CALL MPI_COMM_RANK(MPI_COMM_WORLD, rank)
          IF(rank == 0) THEN
              DO i=1, n
                CALL MPI_ISEND(outval, 1, MPI_REAL, 1, 0, req, ierr)
                CALL MPI_REQUEST_FREE(req, ierr)
                CALL MPI_IRECV(inval, 1, MPI_REAL, 1, 0, req, ierr)
                CALL MPI_WAIT(req, status, ierr)
              END DO
          ELSE IF (rank == 1) THEN
              CALL MPI_IRECV(inval, 1, MPI_REAL, 0, 0, req, ierr)
              CALL MPI_WAIT(req, status)
              DO I=1, n-1
                 CALL MPI_ISEND(outval, 1, MPI_REAL, 0, 0, req, ierr)
                 CALL MPI_REQUEST_FREE(req, ierr)
                 CALL MPI_IRECV(inval, 1, MPI_REAL, 0, 0, req, ierr)
                 CALL MPI_WAIT(req, status, ierr)
              END DO
              CALL MPI_ISEND(outval, 1, MPI_REAL, 0, 0, req, ierr)
              CALL MPI_WAIT(req, status)
          END IF

       This  routine  is  normally  used  to  free  persistent  requests  created  with  either MPI_Recv_init or
       MPI_Send_init and friends. However, it can be used to free a request created with MPI_Irecv or  MPI_Isend
       and friends; in that case the use can not use the test/wait routines on the request.

       It  is permitted to free an active request. However, once freed, you can not use the request in a wait or
       test routine (e.g., MPI_Wait ).

ERRORS

       Almost all MPI routines return an error value; C routines as  the  return  result  of  the  function  and
       Fortran routines in the last argument.

       Before  the  error  value  is  returned,  the current MPI error handler associated with the communication
       object (e.g., communicator, window, file) is called.  If no communication object is associated  with  the
       MPI  call,  then  the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
       handler.  When  MPI_COMM_SELF  is  not  initialized   (i.e.,   before   MPI_Init/MPI_Init_thread,   after
       MPI_Finalize,  or  when using the Sessions Model exclusively) the error raises the initial error handler.
       The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF  when  using
       the  World  model,  or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.  If no other appropriate error handler has been set, then the  MPI_ERRORS_RETURN
       error  handler  is  called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandlerMPI_File_create_errhandler then MPI_File_set_errhandlerMPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_initMPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:MPI_IsendMPI_IrecvMPI_IssendMPI_IbsendMPI_IrsendMPI_Recv_initMPI_Send_initMPI_Ssend_initMPI_Rsend_initMPI_TestMPI_WaitMPI_WaitallMPI_WaitanyMPI_WaitsomeMPI_TestallMPI_TestanyMPI_Testsome

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                               MPI_REQUEST_FREE(3)